As the days are getting shorter, I decided to build some night blades for my mCP X so I can still fly outside in the evenings after work. I took photos as I went just in case they worked and I will share the build step-by-step in this thread.

The one thing I wanted to do differently from other night blades I have seen is that I wanted to use proper battery holders so I didn't have to bother with taping the batteries in and peeling the tape off after I fly.

To drill the holes in the blades, I built a jig out of acrylic. The jig has a slot milled in the top to accept the blade and an indexing pin to position it precisely. There are four holes in the jig to use as guides to drill the blades.

The battery holders fit into the holes drilled in the blades. You can see that the battery holders are facing the leading edge of the blade and angled slightly toward the root so the aerodynamic and centrifugal forces will tend to seat the battery securely in the holder.

Since the holes and the legs of the battery holders are both 0.8mm, they fit snugly. Later, after the copper tape is installed, the tips of the pins that extend through the blade can be folded over and secured with a drop of CA adhesive. I used Loc-Tite 420 so it would wick into the hole, but something thicker might be easier to control.

I used adhesive copper tape, cut into 2mm wide strips as the power conductors for the LEDs. One strip butts up against the side of the battery holder (the positive connection) and the other makes a 60 degree turn and goes under the holder to serve as the contact for the negative side of the battery. This strip continues all the way to the leading edge of the blade and wraps around by a few millimeters to ensure that the end is facing downwind in flight. The bit that wraps around the leading edge of the blade isn't visible in this photo.

The solder joint at the bend in the tape was easy to solder. I just wiped on a little flux with a flux pen, picked up a tiny bit of solder on the tip of the iron and touched it briefly to the joint. The connection to the side of the battery holder was harder. The plastic of the blade outgassed from the heat of the iron and prevented the solder from bridging, so I just cut a tiny piece of 30 gauge wire, tacked it to the tape and the holder and trimmed it flush.

I folded the legs of the battery holder over after applying the tape and then tacked them with CA adhesive after soldering.

I used one blue and one white LED on the top of one blade, and one red LED on the bottom of the other blade. The copper strips continue and wrap around the end of the blade to feed the red LED on the bottom. I extended the tape around both blades to make sure they would remain balanced.

To solder the LEDs, I placed each one on the blade and held it with a piece of Kapton tape for soldering. I put on a bit of flux with a flux pen, picked up a tiny drop of solder on the iron and touched it briefly to the end of the LED and the copper strip. I then removed the tape and soldered the other side. After soldering, I wicked a drop of thin CA under each LED to secure it.

Under certain circumstances, it's possible to see the LEDs on the top and bottom of the disc at the same time, so I placed them so the red ring will appear to be between the blue and white rings.

Most of the mCP X night blades I have seen connect the LEDs directly to the battery without current-limiting resistors. This relies on the Thevenin-equivalent resistance of the CR1216 batteries to limit the current flow. In practice this drains the batteries quickly and it is still possible to exceed the recommended 25mA forward current of the LEDs.

I decided to add series resistors to try to control the current flow. This is complicated somewhat because different colors of LEDs have different forward voltage drops. The red LEDs have a much smaller voltage drop, so they require a larger resistor than the blue and white LEDs, which have a similar, higher voltage drop.

I used a 25 ohm resistor for the parallel blue/white blade and a 50 ohm resistor for the red blade. I cut a small gap in the negative lead near the battery holder and soldered an 0805 SMT resistor across the gap. After soldering, I wicked a drop of thin CA under the resistor to secure it.

In practice, the current flow with new batteries is 20-25mA for each blade, but the red LED is brighter, since all of the current is going through one LED. Having two rings on top seems to make up for this and I think the balance works well in flight.

For orientation lights on the skids, I used the same 0805 SMT LEDs in red and green, each with an 0805 resistor to limit current flow. I used 75 ohm resistors because they'll be running from a 1s LIPO, which delivers a higher voltage than the cr1216 cells on the blades.

I very carefully soldered the resistors directly to the LEDs and then soldered 30 gauge stranded wire to the LED and the resistor. I enclosed the entire package in clear heat shrink tubing and then used a second layer of clear heat-shrink to secure the LED/resistor elements to the tips of the skids. I used 30-gauge solid wire-wrap wire to make tiny twist-ties to hold the wires to the skids.

I soldered a 50 ohm 0805 resistor directly to one lead of the LED, soldered on wires, sealed up the package with black heat-shrink tubing and secured it to the tail with more twist-ties made from 30-gauge wire wrap wire. The tail beacon is very bright. Next time, I'll try a 75 ohm resistor to tame it down a bit.

To get power for the lights, I soldered two battery connectors back-to-back so they can be connected between the battery and the heli, soldered on the wires and covered it all with heat-shrink tubing.

The heli I put these lights on is an HP05 brushless conversion with an XP-7A ESC and twin coreless tail running on Hyperion 550mAH batteries. With stock blades and no lights, it weighs in at 56.28g. With the light kit, ready to fly, it weighs 61.28g, so the whole kit only adds 5g. For a brushless bird, this isn't too bad. It feels a little more stable in the air--probably because of the extra rotating mass.

I expected a lot of wind noise from the battery holders, but as you can hear in the video, it isn't particularly noticeable. The sound is just slightly more ragged than with stock blades, and I expect most of this is turbulence from the LEDs out near the blade tips.

awesome job!!! the battery connector is the best I've seen so far! haven't been wanting to try this for my genius, but didn't want big wraps of tape holding the battery secure; am totally going to try this!

__________________Rockin' the world and flying... that's where i live..

For those of you playing along at home, here is a detailed drawing of the drill guide. A mill with numeric readouts makes locating the holes easy, but one could probably do it with a pair of calipers, a center punch and a steady hand. The drill guide isn't strictly necessary, but it makes it easy to be sure the batteries will be in the same position on both blades.

+1 to this thread being full of win
Here is my mcpx after I redid the rest of the lights.
Oh, and 75ohm and that tail blinky led is still friggin bright as hell.
My luck though my tail motor finally died first time I took it up w/ all the light on it...